Automatic load-dependent brake power regulators are used to adjust the brake pressure in the brake cylinders to the respective load condition of a vehicle. This adjustment takes place automatically in that the respective spring deflection which is dependent upon the axle load or, in the case of vehicles having an air-suspension system, the pressure in the respective air spring bellows which is dependent upon the axle load, adjusts, by means of the brake power regulator, the amount of the brake pressure which is controlled by the motor-vehicle brake valve or, in the case of trailers, by the trailer brake valve.
An automatic load-dependent brake power regulator of the type broadly described above has been proposed in which the brake power regulator is fastened to the vehicle framework and is connected, via a mechanical transmission system comprised of levers and rods, with a metal bellows mounted on the axle. If now there should occur a break at any point in the transmission system, then, due to the weight of the lever and the possibly remaining rod parts, the lever drops down and, when operating the service brake system, the vehicle is braked with a braking force as controlled for an unloaded vehicle, which means insufficient braking in case the vehicle is fully loaded.
There are known types on which, in the event of a break in the transmission system, a spring pulls up the lever of the brake power regulator to the "fully-loaded" position. However, this has the reversed effect of braking an empty vehicle with the braking force as controlled for a fully loaded vehicle, which means excessive braking of the wheels thus causing them to lock. In addition, such a draw spring -- particularly in the case of two-axle assemblies having a stable, relatively heavy linkage system between the two axles -- must be comparatively strong, which is undesirable considering the great possibility that it influences the regulator.
In some countries the dangers described above have been recognized and, therefore, in the European Community it is required that in the event of a breakdown of a valve arrangement which regulates the braking force or of its actuating device, it must be possible to keep a motor vehicle under the conditions as required for auxiliary braking, while for trailers at least 30% of the prescribed service braking effect must be reached.
Since, however, these values as prescribed can be reached only if, in the event of a break in the transmission system, the lever of the brake power regulator is automatically shifted to the "half-loaded" position, the object of the invention is to provide a control mechanism which meets these requirements. This means that a fully loaded vehicle is braked with slightly less force and an empty vehicle is braked with slightly more force. With this solution, which is a compromise, the auxiliary braking action in the case of motor vehicles and 30% of the service braking action in the case of trailers is reached as required by the guidelines of the legislators.